494 APPENDIX 



cut open the lung will be seen to be a hollow sac with corru- 

 gated walls (Fig. 282). 



" Plucks " obtained from a butcher will illustrate the struc- 

 ture of the mammalian larynx, trachea, bronchial tubes, etc. If 

 fresh and not punctured with the knife they may be inflated. 

 To work well they should be kept moistened (Fig. 283). 



The presence of carbon dioxide in the air exhaled from the 

 lungs may be shown by using limewater or baryta water, with 

 either of which carbon dioxide forms an insoluble precipitate, 

 which at first floats as a delicate white film on the surface of 

 the liquid. Pour some of the fluid into a saucer or watch glass, 

 then breathe heavily upon it a few times through the mouth, 

 and the film will be formed. 



CHAPTER XVIII 



The structure of the kidneys is well illustrated by the kidney 

 of the sheep. Several of these should be procured and opened 

 in various directions to show the structure (Fig. 290). 



CHAPTER XIX 



With little trouble skeletons of frogs, birds, and mammals 

 with bones connected by flexible attachments may be prepared. 

 Carefully cut away all of the muscles and other soft parts, leav- 

 ing only the ligaments connecting the bones. Then place the 

 roughly prepared specimen for one or two weeks in Wicker- 

 sheimer's fluid, which is prepared as follows : In three liters of 

 boiling water dissolve 100 grams of alum, 60 grams of caustic 

 potash, 25 grams of salt, 12 grams of saltpeter, and 10 grams 

 of arsenic. Cool and filter the liquid. Then to each liter of 

 the fluid add 400 cubic .centimeters of glycerine and 100 cubic 

 centimeters of alcohol. The ligaments of skeletons soaked in 

 this fluid will remain flexible during many months of exposure 

 to the air. Should the ligaments become stiffened, their flexi- 

 bility may be restored by a few hours' immersion in the fluid. 



